Printable, heat-bondable sheet material

ABSTRACT

A laminated sheet material comprising (1) a porous, printable thermoplastic polymeric layer and (2) a heatactivated adhesive layer has particular utility in preparing call number labels for attachment to the spines of books. The physical properties of the two layers are interrelated, and the heat which activates the adhesive during application of the label also indelibly seals the indicia in the printable layer.

United States Patent [191 La Perre et a1.

[ PRINTABLE, HEAT-BONDABLE SHEET MATERIAL [75] Inventors: James D. La Peri-e, Troy, Wis;

James F. Dyrud, North St. Paul; Thomas W. Zosel, St. Paul, both of Minn.

[73] Assignee: Minnesota Mining and Manufacturing Company, St. Paul, Minn.

[22] Filed: Apr. 28, 1971 [21] Appl. No.: 138,216

[52] US. Cl. 161/167, 117/122 H, 117/122 P, 161/150, 161/229, 283/64 [51] Int. Cl. C09j 7/02, C09j 7/00 [58] Field of Search 283/64; 281/1; 11/10; 161/150, 161/167, 252, 229; 117/122 11,122 PA, 122 P, 11, 15; 260/897 B, 30.8 R; 264/45, 49

[ 1 Feb. 5, 1974 Mfc. of Bookcovers of Tyvek, duPont Tech. Information Bul. S-3 (Mar. 1970) pp. 3-7.

The Properties & Processing of TYVEK, Spunbonded Olefin (Bul. S-8-Dec. 1970) (pp. 3-12).

Primary Examiner-George F. Lesmes Assistant ExaminerM. B. Wittenberg [57] ABSTRACT A laminated sheet material comprising (1) a porous, printable thermoplastic polymeric layer and (2) a heatactivated adhesive layer has particular utility in preparing call number labels for attachment to the spines of books. The physical properties of the two layers are interrelated, and the heat which activates the adhesive during application of the label also indelibly seals the indicia in the printable layer.

6 Claims, 4 Drawing Figures [56] References Cited UNITED STATES PATENTS 2,416,668 3/1947 Schroeder 260/30.8 R 3,262,996 7/1966 Kurtz et al. 260/30.8 R 3,595,739 7/1971 Meyer 161/229 PRINTABLE, HEAT-BONDABLE SI-IEET MATERIAL BACKGROUND OF THE INVENTION This invention relates to adhesive-coated printable sheet material having particular utility for the preparation of label stock which will bond firmly to polymeric surfaces.

The invention has utility in the preparation of tamperproof identification cards, library cards, etc., but is especially useful in the preparation of call number labels for library books. Accordingly, it will be described in connection with this use.

Librarians concerned with the accession of library books have had to cope with applying call numbers for many decades. At first, librarians merely applied call numbers and other indicia to the books with a marking pen, a variation involving the use of a stylus to apply the indicia by transfer of gold leaf coated on a temporary carrier sheet. Occasionally the gold leaf was replaced by a layer of pigment in a thermoplastic binder, an electrically heated stylus being used to transfer markings. In each of these methods, the hand-lettered labels are necessarily non-uniform, especially if applied by different librarians. Further, for adequate adhesion, it is generally necessary to prime the book surface with a plastic spray, apply a plastic coating over the indicia, or both.

A more refined transfer coating method involves the use of individual preformed letters, temporarily mounted on a carrier sheet and transferred to the book backing. Although the resultant labels are uniform in appearance, the labeling process is slow and subject to the same priming and/or fixing requirements.

Call letters have also been typed or printed on paper of cloth lables, which are thereafter adhered to the book by either a self-contained or a separately supplied water-soluble or pressure-sensitive adhesive. Neither type of adhesive, however, adheres especially well, and, in many instances the adhesive embrittles with age. Further, the indicia applied to the labels tend to smear with handling unless a fixative spray is applied.

The use of hot melt or other types of heat-activated adhesive eliminates some of the bonding problems described in the preceding paragraph but fails to solve others. One label employs a polyvinyl fluoride film having a slightly tacky heat-activatable adhesive on one face and carried by a removable liner. The call numbers are typed on the film, a mattefinish cellulose acetate tape applied over the indicia to prevent smudging, and the resultant laminate heat-bonded to a book. Another commercially available' article uses a flattened plastic sleeve having a heat-activated adhesive on one face. Call letters are typed on a paper or cloth lable, which is inserted in the sleeve, and the assembly then heat-bonded to the book. Although attractive and functional, each of these labels is not only inherently expensive but also requires at least two steps to apply.

In this well-worked field, the present inventor has come forward with a simple, inexpensive, and highly effective contribution to the art.

SUMMARY The present invention provides a novel sheet material which can be readily marked with uniform indicia and conveniently applied to book covers. After application,

the label is firmly bonded, resistant to smudging, and highly abrasion-resistant. No priming, fixing or indiciaprotecting tape application is necessary. The characteristics which make the sheet material useful for labeling books also make it useful for preparing library cards, tamperproof identification cards, credit cards, etc.

The invention is a composite sheet material comprising superposed and adhered plies of (1) an inkreceptive printable layer and (2) solvent-free heatactivatable adhesive layer, the physical characteristics of the two layers being interrelated. Desirably the adhesive layer is somewhat tacky prior to heat-activation to facilitate positioning of the composite sheet material on the substrate to which it is to be bonded.

The printable layer is on the order of l0-500 microns thick, having an exposed porous surface of thermoplastic polymeric material at least 10 microns thick. When formed into a mirror-smooth film the thermoplastic polymeric material has a critical surface tension of at least 29 dynes/cm. The thermoplastic material fuses in the approximate range of to 200C., and the fused thickness of the entire printable layer is on the order of 5 to 250 microns. Printed indicia applied to the printable layer have, after the sheet material is bonded to a substrate, an abrasion resistance of at least 700 cycles.

The adhesive layer has a thickness on the order of lO- microns. At 20C., it has a 1 second shear creep compliance of less than about 1 X 10 cm /dyne, and at the fusion temperature of the printable layer, the adhesive has a 10 second shear creep compliance in the approximate range of l X 10 cm /dyne to l X 10* cm /dyne and an elastic response less than 45 percent of the total 10 second response.

When the adhesive layer is formed into a 75 micron film and heat-laminated between two smooth identical micron polymeric films of isotactic polypropylene, unplasticized polyvinyl chloride, polypyromellitimide, and cellulose nitrate, it displays a T-peel adhesion value of at least 1 kilogram per centimeter, in at least one instance.

The terms critical surface tension, tance," shear creep compliance,

abrasion resiselastic response and T-peel adhesion refer to either standard or empirical tests, each of which will be described in the immediately subsequent section.

To illustrate the manner in which the sheet material of the invention is used, call numbers or other identifying marks are applied to the printable layer with a conventional typewriter. The label is then placed on the spine of a book, the adhesive layer being in contact therewith. A thin film of temperature-resistant low surface energy polymer, e.g., polytetrafluoroethylene, is then laid over the printed surface, and a heated iron applied thereover. The surface of the iron is heated to approximately 25C. above the fusion temperature of the polymer in the printable layer. During pressing, the adhesive layer activates and bonds to the spine of the book, while the polymer in the printable layer fuses, thereby sealing the indicia into the printable layer. The iron is then removed and the interposed low surface energy film removed.

DESCRIPTION OF PHYSICAL TESTS Critical Surface Tension When a drop of liquid is placed on a plane horizontal solid surface and a tangent to the drop drawn at the point of contact with the plane, the angle formed between the plane and the tangent is commonly referred to as 0. If cosine 0, measured with liquids having a variety of surface tensions, is plotted against the surface tension of these liquids, a nearly linear relationship is seen to exist. If a straight line is drawn through the points and extrapolated to cosine 1.0, the intercept is chosen as the critical surface tension, y of that solid. This subject is discussed in greater depth in Chapter 1 of Contact Angle, Wettability, and Adhesion, Advances in Chemistry Series 43, American Chemical Society.

In determining y, for the polymer making up the printable surface layer, the polymer is cast into a mirrorsmooth film which is maintained in scrupulously clean condition. If y, is less than 29 dynes/cm, it is found that the printable surface layer is poorly receptive to solid inks.

Abrasion Resistance This is an empirical test designed to measure the inherent abrasion resistance of the printable layer and, indirectly the ink penetration of any part of a character. To some extent the test integrates the qualities of porosity, compressiblity, and surface roughness. In accordance with this test, an IBM Selectric typewriter provided with an Orator" style ball (No. 10) with the impression selector set at 5 (the highest letter impact force) is used to apply upper case letter Ms over the surface of a 10.8 cm diameter disc, the letters being separated by a single space in each horizontal line, and the lines being triple spaced. Three adjacent Ms in a horizontal line are deemed a label. After the entire disc is thus prepared, a smooth 50 micron polytetrafluoroethylene film is placed over the surface of the layer and a flat iron, having a power density of 3.1 watts/cm and set at 30C. above the fusion temperature of the printable layer, is applied with a force of 140 gms/cm for seconds. The disc is then mounted on a Taber Abraser in accordance with the general procedure specified in ASTM Test D-1044-56. In this test, a CS-l7 Calibrase" abrasive wheel abrades an annular path approximately 1.3 cm wide centered 3.8 cm from the center of the disc, so that its path crosses 12-16 labels. A force of 250 grams is applied to the abrasive wheel, which is refaced before each test by running it for 50 cycles on Grade 150 silicon carbide coated abrasive. The disc is examined every 100 revolutions. When any portion of an M is completely abraded away, the label containing that M is considered unacceptable. The lowest number of cycles at which all labels on a disc are unacceptable is reported; to be acceptable, a disc should successfully survive 700 cycles. If a disc survives 1,400 cycles, the percentage of unacceptable labels is reported. In each case, the value reported is the arithmetic mean of three identical discs. It is believed that 200 cycles roughly corresponds to one years library use for a fairly heavily circulated book.

Stiffness of printable layer Stiffness can be measured on a Taber V-5 stiffness tester, Model 1508, according to Tappi Standard T-489 08-70. In this test one narrow edge of a 3.8 cm X 7.6 cm sample of sheet material is gripped by jaws connected to the axis of rotation of a pendulum. Sufficient force is then applied to flex the cantilevered end of the sample 15, the resistance to bending being transmitted to, and thereby deflecting, the pendulum. The amount of deflection is converted to Taber Stiffness Units, i.e.,the number of 200 mg units which, if

proximately 1r radians/inch curvature), the stiffness value should not exceed 10. On the other hand, for

thicker books or application to flat stock, stiffness is of relatively minor importance.

Fusion temperature 2.54 cm X 7.62 cm samples of printable layer are laid parallel and overlapped so that a 2.54 X 2.54 cm area is in contact. A 50 micron polytetrafluoroethylene film is placed on each side of the layup, which is supported on a horizontal surface. A platen heated to C. is then superposed over the overlapped area under a force of 907 grams for 10 seconds and removed. The polytetrafluoroethylene films are removed, the ends of the two samples are clamped in opposite jaws of a tensile tester, and the force required to separate the two samples measured at a jaw separation rate of 25.4 cm/minute. If the separation force does not exceed 200 gms/cm width, the procedure is repeated at 5C. increments. The lowest temperature at which this force is attained is deemed the fusion temperature. The fusion temperature should be low enough to minimize power consumption and reduce danger to personnel applying labels, but high enough to preclude the possibility of the labels distortion when the book to which it is attached is placed on a hot radiator, exposed to direct sunlight, etc. It has been found that the approximate range of 100C. to 200C. meets these criteria.

Creep Compliance of Adhesive Layer Arthur V. Tobolsky in Properties and Structure of Polymers, John Wiley & Sons, Inc., 1960, Section 6, discusses the five regions of viscoelastic behavior possessed by linear amorphous polymers. In so doing, he characterizes the elastic properties of a polymer by measuring its tensile modulus (13,) as a function of temperature for a specified period of time. As a polymer is heated, it successively passes through regions which can be designated as glassy, transition, rubbery plateau, rubbery flow, and liquid flow. Only the latter two regions are of significance to the present invention. For a 10 second loading time, the dividing line between the rubbery plateau and the rubbery flow regions is E, 2.5 X 10 dynes/cm In the rubbery flow region, the shear modulus (G,) is one-third the tensile modulus, or 0.83 X 10 dynes/cm at 10 seconds. Shear creep compliance (J which is the reciprocal of the shear modulus, is 1.2 X 10" cm ldyne for the boundary between the rubbery plateau and rubbery fiow regions.

In measuring shear creep compliance, the adhesive to be tested is spun-cast on a smooth film of polytetrafluoroethylene to a thickness of 500 microns. Two test pieces of equal area are then die cut from the adhesive sheet and placed in a parallel plate shear creep plastometer*,( See, e.g., Ferry, John D., Viscoelastic Properties of Polymers, John Wiley & Sons, Inc., New York, N. Y., 1961, Chapter 6.) one piece being on each side of the center plate, with an outer plate contacting the exposed surface of each. Screws connecting the two outer plates are then tightened so as to compress the adhesive layers 10 percent. The parallel plates are placed in horizontal arrangement in an oven and one end of the center plate connected to a linear displacement voltage transformer, which in turn is connected to a chart recorder. A hook is then attached to the opposite end of the center plate, a flexible wire extending from the hook over a pulley, while the outer plates are held in fixed position. The oven is raised to the desired temperature and stabilized there at i 05C., after which a suitable weight to 1,500 gms, whatever will both measurably deform the sample and remain within the linearity limit of the sample) is attached to the free end of the wire, and the chart recorder started. From the chart recorder the time and displacement can be read and the shear compliance, 1, of the adhesive at a given temperature calculated from the equation where t is the time at which the measurement is taken, A is the area of one face of one of the adhesive samples, h is the thickness of one of the adhesive samples, Xi is the displacement at time t (where X,- is less than h), and F is the force due to gravitational acceleration of the mass attached to the wire connected to the middle plate. When A is expressed in cm*, h in cm, X, in cm, and F in dynes, I is given in cm /dyne.

Per cent Elastic Response The simple shear creep compliance (I can be expressed as the sum of three components (J .I +n), where I is the elastic compliance, J is the delayed elastic compliance and 1; is Newtonian viscous flow. We can estimate the elastic portion of the total response from the chart recorder output curve (a plot of deformation against time) which is used to calculate J A typical output curve shows that during the initial time of the experiment the slope of the curve remains nearly constant. At the point where the curve deviates from this constant slope, the viscous components of the polymer become detectable. (The viscous components include both the delayed elastic compliance .I and viscous flow n). The percentage which the deformation (X,) at this point bears to the total deformation at 10 seconds (X seconds) is a measure of the amount of elastic response the adhesive exhibits for a 10 second loading time. If the percentage of elastic response exceeds 45 percent, the adhesive layer tends to retract after the heat source is removed, causing a label to loosen or pop off.

T I eel Kantian I A 75 micron film of the adhesive to be used in the adhesive layer is formed and heat-laminated for ID seconds at a pressure of I40 gms/cm between pairs of smooth identical 150 micron polymeric films of 1) isotactic polypropylene, (2) unplasticized polyvinyl chloride, (3) polypyromellitimide, and (4) cellulose nitrate (pyroxylin), a portion of each pair of films extending beyond the adhesive. The lamination temperature is set at the fusion temperature of the printable layer with which it is intended that the adhesive layer will be used. A l centimeter strip of the resultant laminate is then prepared, the two unjoined ends placed in opposite jaws of a tensile machine, and the jaws of the machine moved apart at the rate of 25.4 cm per minute. The force required to separate the films from the adhesive should be at least one kg/cm for at least one of the pairs of films in order for the invention to adhere effectively to the conventional covers of books.

BRIEF DESCRIPTION OF THE DRAWINGS Understanding of the invention will be facilitated by I referring to the accompanying drawings, in which like numbers refer to like parts in the several views, and in which:

FIG. 1 depicts an enlarged and somewhat stylized view of one embodiment of the invention;

FIG. 2 is a view of the article of FIG. 1 after it has been subjected to heat and pressure sufficient to fuse the printable layer;

FIG. 3 depicts another embodiment of the invention; and

FIG. 4 is a view of the article of claim 3 after it has been subjected to heat and pressure.

DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS The nature of the invention will now be further pointed out with the aid of illustrative but non-limiting examples, in which all parts are by weight unless otherwise noted. For convenience, component printable layers are shown in Table I, adhesive layer formulations are shown in Tables II, adhesive characteristics are shown in Table III, and various combinations thereof are shown in Table IV.

TABLE I PRINTABLE LAYERS Fusion Critical Abrasion Stiffness temp. sur fa c.e resis- (Taber Desig- Thickness, microns C. Tension, 7 tance, Stiffnation Composition Unfused fused dynes, cm cycles ness Units) I A Spun-bonded I25 I35 31 MOO-82% 0.9

polyethylene fibers( I) I B I A treated I25 65 I35 30 MOO-82% 0.9

with 5% poly (vinyl ethyl ether) solution (2) I C Isotactic I I60 I63 29 700 3.2

polypropylene film-solvent treated (3) l D Porous iso- I80 I62 29 I000, 2.9

tactic polypropylene film and leached) (4) i "TXBLE i-Continued 7 W PRINTABLE LAYERS Fusion Critical Abraison psurface resis- Stifi'ness Desig- Thickness, microns C. Tension, 7c, tance, (Taber Stiffness nation Composition Unfused fused dynes, cm cycles Units) "5 Porous salt- 150 75 171 39 800 3.7

leached polyvinyl chloride film (5) IF l 0.1 [G 250 125 14.5

(I) Tyvek (Reg. T.M.) 1043 (2) EDBM Poly(vinyl ethyl ether) Bakelite Co.

(3) Made according to teachings of US. Patent 3,135,622

(4) 100 parts polypropylene flake [hercoflat (Reg. T.M.)], 0.2 part amine antioxidant [Plastanox H61], 200 parts 30 micron NaCl, 30 parts TiO, pigment and i0 parts paraflin oil are dispersed, fused, milled and calendered to a thickness of 180 microns. The NaCl is then leached out in warm water.

(5) I00 phrs. medium molecular weight polyvinyl chloride, parts dioctyl phthalate plasticizer, 3 parts Ba/Cd stabilizer [Mark (Reg. TM) I80]. 0.25 pan stearic acid lubricant, parts TiO, pigment, and 200 parts NaCl are processed as in (4) to form a ISO-micron porous film.

Table Il ADHESIVE LAYER COMPOSITION Tackifiers Plasticizer Crosslinker Desig- Elastomer nation l00 pts) Parts Type Parts Type Parts Type Parts Type Parts Type II A :40 80 Medium 20 Mixture of 50 Glycerol- 50 Liquid :30

butadiene: hard 0- and presin acid butadiene: acrylonitrile parasultoluene ester (4) acrylonitrile rubber copolymer fonamide sulfona- (5) Mooney resin (2) mide (3) viscosity i0 l 11B 20 l0 2O I00 IIC 8O 20 20 p-te r t butyl phenol formaldehyde resin (6) rip 80 20 30 I] E Same as II A Mixture of Aromatic Dioctyl phthalate l but contains and pketgr gg 30 parts TiO toluene resin mp. pigment in sulfona- 80C; addition to mide Acid elastomer value- (l30 parts neutral; total) Specific Grav.

l.l7l.2

. W fl F 60:40 so 0.95 ulrur butadiene: 0.05 benzo- ML acrylonitrile thiazyl copolymer disulfide M2911 accelerator 80-1 to vv g 1T6 50 0.095 Sulfur 1005 accelerator (same as II "Tl Polyethyll5 Partially acrylate hydromethanol lyzed precipitated 91:9 vinyl LV. 1.92 chloride:-

vinyl acetate copolymer (9) 1T Polyethylacryl5 Partially I5 Dioclyl sebum late, methanol hydroprecipitated lyzed Lv. 1.92 91:9 vinyl chloride:

vinyl acetate copolymer (9) Considering the drawings in more detail, composite sheet material of FIG. 1 comprises printable layer 11 and slightly tacky heat-activatable adhesive layer 12, release sheet 14 being provided to facilitate handling. Layer 11 is a highly porous nonwoven mat of very fine thermoplastic fibers, to which ink marking 13 has been applied, the ink thereof partially penetrating layer 11. FIG. 2 depicts the result of removing release sheet 14, placing adhesive layer 11 in contact with substrate l5, e.g., a book, and subjecting composite sheet material 10 to heat and pressure above the fusion temperature of the thermoplastic fibers. It will be noted that the upper surface of layer 11 is smooth and that the body of layer 11 has fused into a thin film, into which marking 13 has been sealed. In the process, heatactivatable adhesive layer 12 has also softened sufficiently to adhere to substrate 15.

.99. P1..knsuLfil -s sfins r v -stem"; techniques; one way of preparing a suitable surface is described in US. Pat. No. 3,135,622. FIG. 4 is analogous to FIG. 2, showing the result of subjecting composite sheet material to heat and pressure above the fusion temperature of thermoplastic film 31, thereby flowing the etche d surface and sealing marking 33 into film 3 l.

In forming composite sheet material in accordance with the invention, the following procedure was observed: With the exception of 11 C and II D the adhesives listed in Tables II and III above were coated on silicone-coated kraft paper liners and partially dried to between percent of dryness. One of the printable layers from Table I was then superposed, the resulting layup passed through squeeze rolls, and the remaining solvent evaporated. Adhesives IIC and IID, II F and II G were dried to essentially percent and then heated at 155C. for 1 hour. The surface of the adhesive was then softened with a volatile solvent, a printable layer from Table I superposed, the resulting layup passed through squeeze rolls, and the solvent evaporated. Several illustrative combinations are set forth in Table IV; it will be noted that some of these combinations conform to the parameters of the invention and some donot TABLE IV COMBINATIONS OF VARIOUS PRINTABLE LAYERS FROM TABLE I WITH ADHESIVE LAYERS FROM TABLE II Adhesive layer II A invention yes IA IIB no II C yes II D no yes II E yes II F no Suitable for Comments Similar to FIG. I. Illustrates an acceptable adhesive very near the limit of .I 20C.

Adhesive is too soft; i.e., .l 20C is greater than 0.7 X 10' cmldyne. Also T-peel value is too low for all substrates.

Sheet material has been treated to increase ink receptivity. Adhesive is within limits. Adhesive soft enough to form bond at the fusion temperature of I B but elastic response is too high. Thus, the adhesive dewets" the substrate when application pressure is removed, giving a low T-peel value.

Similar to Example 4.

Fusion temperature of II D nearly the same as II C; therefore unacceptable as in Example 5. Value of J at 52C is included in Table III to illustrate that a bond will form if I is greater than 0.9 XIO" cm/dyne and elastic response is less than 45% as is the case with adhesive II E at 52C. Similar to FIG. 2. Illustrates that if adhesive is acceptable with printable layer that fuses at C, then it is also acceptable with a printable layer that fuses at a higher temperature since normally I t, will decrease and elastic response will decrease as temperature increases. (An exception occurs where crosslinking is taking place at a faster rate than softening with increased temperature, as in Examples 4 and 5.) Similar to Example 4 except crosslinker is sulfur instead of phenol. elastic response is too great even though I polymer blend will "wet out" the TABLE IV Continued TABLE ll Printable Adhesive Suitable for Example layer layer invention Comments substrate. l l C or II F no Even at l62-l63 C the elastic l D response of the adhesive is too high. l l l E ll F no Same as in Examples 9 and l0. I2 I A or ll G yes Approximates permissible limit for l B elastic response limit.

I3 I C ll G yes Bond strength increased over value in Example l2 since elastic response is lower.

14 I ll 0 yes Similar to Example 7.

l5 IA or II H yes Chemically different adhesive lB from llA-llG. I6 I A or ll J no Adhesive too soft. J 20C I B is greater than 0.7

X lO em /dyne and T-peel is too low. 17 l A or ll K yes Another chemically different l B adhesive. l8 lA or ll L no Shear compliance of adhesive 1 B .l my less than 0.9 X 10' cm dyne. elastic response also too high. T-peel too low 19 l C I] L yes lC printable layer has higher fusion temperature than I A or I B, improving adhesive characteristics.

20 l A or ll M no T-peel values all too low.

B 2l l A or ll N yes "Grater/"areas EdffibifiifibiiSEEiBuTiTfTblETVfihE M one identified as Example 8 has been found especially satisfactory. The printable layer is flexible and quite ink-receptive, and the titanium dioxide imparts whiteness to the underlying adhesive layer, thereby enhancing the readability of markings. The adhesive layer is slightly tacky at room temperature, facilitating positioning the label on a book prior to applying heat to effect fusion and bonding; it also adheres well to polyvinyl chloride and cellulose nitrate, both of which are common coatings for book covers.

We claim: 7 7 W l w l. cofiiififiet material having particular utility in the formation of a smudge-resistant, durable easily applied labels for imparting library system designation to the spines of books, comprising in superposed adherent contact,

(1) an ink-receptive printable layer having a. a thickness on the order of 10 to 500 microns and b. an exposed porous surface of fibrous spun bonded thermoplastic polymeric organic material which i. when formed into a mirror-smooth film has a critical surface tension of at least 29 dynes/cm, and ii. has a thickness of at least 10 microns, c. a fusion temperature in the approximate range of 100 to 200 C., d. a fused thickness on the order of 5 to 250 microns, and e. an abrasion resistance of at least 700 cycles, and 2. a solvent-free layer of lieat-activatable adhesive selected from the class consisting of l) a blend of rubbery butadienezacrylonitrile copolymer, sulfonamide resin and tackifier, (2) thermoplastic polyurethane, (3) thermoplastic poly(vinyl alkyl) ether mid l tackified polyethylacrylate elastomer and having a. a thickness on the order of 10 to microns,

b. at the fusion temperature of said printable layer, =5 lo-sec o nd shear creep compliance in the approximate range of l X 10 cm /dyne to 1 X 10 cm /dyne,

c. an elastic response of less than 45 percent,

cl. at 20C., a 1 second shear creep compliance of less than 0.7 X 10 cm /dyne, and

e. when formed into a 75 micron film and laminated at the fusion temperature of said printable layer, between two smooth identical micron polymeric foils of isotactic polypropylene, unplasticized polyvinyl chloride, polypyromellitimide and cellulose nitrate, a T-peel adhesion value of at least 1 kg/cm in at least one instance.

2. The sheet material of claim 1 wherein the adhesive layer is mildly tacky and protectively covered by a removable liner.

3. The sheet material of claim 1 wherein the inkreceptive layer is formed of fibrous spun bonded high density polyethylene.

4. The sheet material of claim 3 wherein the spun bonded polyethylene is saturated with a poly(vinyl alkyl ether).

5. The sheet material of claim 4 wherein the adhesive is a blend of a rubbery acrylonitrilezbutadiene polymer containing 2545 me] percent acrylonitrile, sulfonamide resin plasticizer, and tac ifier.

6. A book having a heat-bonded to its cover a label formed from the sheet material of claim 1.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N07 3,790,139 Dated 2-5-7 Inventofls) James D. LaPerre. James F. Dyrud and Thomas w. Zosel It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 37, "lables" should be labels line 55,

",lable" should be label Table II Designation IIE, change the entries under Columns 3-9 to read as follows:

Parts Type I Parts Type Parts Type Parts 10- 10 Mixture 80 Aromatic 2 of oand ketone ptoluene resin mp.

sulfonamide 80C;

Acid valueneutral; Specific Grav. l.17-l.2 (7) After Table ll, in the footnotes, 5th line "(z)" should be Table IV, Example 9, under "Comments" column, 4th line after "'J sec)" insert is in the range where the Column 13, claim 1, line 62, "2." should be (2) Signed and sealed this 10th da of September 1974.

(SEAL) Attest:

MCCOY GIBSON, JR. C. MARSHALL DANN Attestlng Officer Commissioner of Patents FoRM po-uoso (IO-69) U'SCOMWDC sowmp'og Column 1H, claim 5, line 61, "tac ifier" should be tackifier 

2. a solvent-free layer of heat-activatable adhesive selected from the class consisting of (1) a blend of rubbery butadiene: acrylonitrile copolymer, sulfonamide resin and tackifier, (2) thermoplastic polyurethane, (3) thermoplastic poly(vinyl alkyl) ether and (4) tackified polyethylacrylate elastomer and having a. a thickness on the order of 10 to 125 microns, b. at the fusion temperature of said printable layer, a 10-second shear creep compliance in the approximate range of 1 X 10 6 cm2/dyne to 1 X 10 3 cm2/dyne, c. an elastic response of less than 45 percent, d. at 20*C., a 1 second shear creep compliance of less than 0.7 X 10 6 cm2/dyne, and e. when formed into a 75 micron film and laminated at the fusion temperature of said printable layer, between two smooth identical 150 micron polymeric foils of isotactic polypropylene, unplasticized polyvinyl chloride, polypyromellitimide and cellulose nitrate, a T-peel adhesion value of at least 1 kg/cm in at least one instance.
 2. The sheet material of claim 1 wherein the adhesive layer is mildly tacky and protectively covered by a removable liner.
 3. The sheet material of claim 1 wherein the ink-receptive layer is formed of fibrous spun bonded high density polyethylene.
 4. The sheet material of claim 3 wherein the spun bonded polyethylene is saturated with a poly(vinyl alkyl ether).
 5. The sheet material of claim 4 wherein the adhesive is a blend of a rubbery acrylonitrile:butadiene polymer containing 25-45 mol percent acrylonitrile, sulfonamide resin plasticizer, and tac ifier.
 6. A book having a heat-bonded to its cover a label formed from the sheet material of claim
 1. 